Preparation of pure aromatics from petroleum distillates



Jan. 13, 1948. w. H. cLAUssx-:N Er AL 2,434,395

PREPARATION OF PURE AROMATICS FROM PETROLEUM DISTILLATES Filed March 17,1942 Patented Jan. I3, 1948 PBEPARATIGN F PURE AROMATICS FROM PETROLEUMDISTILLATES William H. Claussen and Thomas M. Powell,

Berkeley, Calif., assignors, by mesne assignments, to CaliforniaResearch Corporation, San

, Francisco, Calif., a corporation o! Delaware Appummn Mms rz, 1942,semi No. 494,994

12 claims. (c1. 26o-ess) 'I'his invention pertains to the production ofaromatic rich hydrocarbon liquids from petroleum distillates and isdirected more particularly to the production of substantially purearomatics from selected hydrocarbon distillates by means of a novelcombination sequence of catalytic and distillation steps.

Various methods have hitherto been proposed for extracting, by means ofselective solvents, the aromatic compounds occurring in certain naturalpetroleumS. Methods have also been disclosed for converting a portion ofthe nonaromatic materials in petroleum distillates to aromatics, whichmay-then be separated by means of selective solvents. just as in thecase of the originally occurring aromatics.

While the aromatic compounds present or produced in petroleum fractionsmay be substantially concentrated through the use of known methods ofsolvent extraction, it is, however, unfortunately a fact that no knownsolvent is sufilciently selective to recover by a simple operation allof an aromatic compound from admixture with the associated parainic andnaphthenic materials in a petroleum distillate and at the same time torecover it in a state of suiliclently high purity that it may besubjected directly to nitration as, for instance, in the preparation ofexplosives, or may be used directly as raw material in other specicchemical processes.

We have now discovered a particular method of operating catalytic steps,which are already more or less well known in connection with thereforming of gasolines and naphthas for their antiknock improvement, bymeans of which it is possible to produce substantially pure aromaticcompounds, such as benzene. toluene, ethyl benzene and xylene, fromappropriately chosen fractions of petroleum. No complicated solventextraction procedure is employed in our process, the appropriate stepsof catalytic conversion properly related to simple distillationprocesses being adequate to produce aromatics of better than 99% purity.For instance, it has been found possible by means of the particularcombination of process steps which constitutes our invention to convert,a, toluene cut," boiling from about 180 to about 240 F., from aCalifornia straight-run petroleum distillate, simply and directly intonitration grade toluene with yields of the order of 40% by weight. Whilethe exact yield will depend to a certain extent upon whether the crudeoil from which the charge is taken is of the naphthenic, mixedbase orparafnic type, the process of our invention is applicable to all typesof petroleum though a substantial content of cyclic compounds isdeslrabe for best yields.

It is the object of the present invention to provide a relatively simplecatalytic process by means ci' which it is possible to prepare lowboiling aromatic compounds from petroleum fractions with a higher degreeof purity and in substantially improved yields over hitherto knownprocesses.

It ls a more specic object of the present invention to provide acatalytic process wherein catalytic conversion steps are correlated withsimple distillation operations in a manner such that selected petroleumdistillates may be converted to substantially pure aromatic compoundswith relatively high yield.

It is a still more specic object of the present invention to provide acatalytic process for converting selected petroleum fractionssubstantially to aromatic compounds wherein two coordinated stages ofcatalytic treatment are employed in series with a fractionation stepinterposed between them.

It is another specic object of the present invention to provide a methodfor converting a.

selected petroleum fraction to substantially pure aromatic compounds bycatalytically preparing an aromatic rich distillate, separating it fromnon'- aromatic compounds so far as practical by fractional distillationand subjecting the so separated fraction to a second catalytic treatmentfor conversion of the residual nonaromatic compounds.

It is a more specific object of the present invention to provide aprocess for preparing substantially pure toluene from a petroleumhydrocarbon fraction boiling between about and 235 F. and containing asubstantial proportion of naphthenic compounds.

Other and more specific objects of the invention will be apparent fromthe following description and' the appended claims.

While it is conventional practice in most chemical reactions, andparticularly in the catalytic processing of hydrocarbons such as incatalytic cracking and catalytic reforming operations, to separate fromlthe product unreacted components of the charge for return to thereaction in order that the highest possible yield of the desired productmay be realized from each unit of charge, it is not conventionalpractice to segregate a fraction of the reaction mixture rich in thedesired product, and boiling substantially Within the same range as theoriginal charge, for the purpose of subjecting it to a. second stage ofcatalytic treatment, which may be substantially similar to the rststage. and to thereby effect a substantial purication and some increasein yield of the desired product. It is believed that this element ofnovelty is highly signicant and is in large part responsible for thepeculiar advantages of the process of the present invention.

Broadly considered, our process for producing substantially purearomatic compounds from selected petroleum distillates may be dividedinto four signicant and critically related steps, namely a iirst stagecatalytic step, an interstage separation step, a secondstage catalyticstep and a final separation step.

In the catalytic stages we have found that quite a number of reformingdehydrogenation and/or cyclization catalysts, someA of which are alreadymore or less well known, may be employed with qualitatively the sameresult. For instance, molybdenum oxide, vanadium oxide, chromium oxide,aluminum oxide, zinc oxide and various specific adaptations andcombinations of these oxides, such as molybdenum oxide or vanadium oxidesupported on activated alumina or the complex substances formed whenmolybdenum and aluminum, vanadium and aluminum or zinc and aluminum ionsor other soluble forms of these elements are coprecipitated from anaqueous solution of their appropriate salts, as by the addition ofammonia, have been successfully employed as catalysts in the process ofthe present invention. We have also found that the same or differentcatalysts may be employed in the rst and second stages of the process.For instance, a catalyst consisting of molybdenum oxide supported onactivated alumina may be employed in both stages or it may be employedonly in the first stage, while a catayst comprising vanadium oxidesupported on activated alumina may be used in the second stage or thecoprecipitated catalysts mentioned above may be similarly employed.

In a preferred embodiment of the process of the present invention acatalyst in which a molybdenum component and an aluminum component,coprecipitated from a solution containing soluble salts of the twometals, is employed in both the first and second stages. In anotherpreferred embodiment we employ the same molybdenum containing catalystin the rst stage and a similarly coprecipitated catalyst containingvanadium and aluminum in the second stage with very satisfactoryresults.

In carrying out the process of the present invention, when it is appliedto the production of pure toluene for nitration or'use as a raw materialin other chemical processes, we prepare a distillate from naturallyoccurring petroleum by close fractionation to give a, cut boiling fromabout 180 to 235 F. This stock is charged to an appropriate firstcatalyst stage employing one of the above-mentioned catalysts and issubjected therein to a temperature between about 800 and 1050 F. in thepresence of a carrier gas containing a substantial proportion ofhydrogen and at a total pressure of the order of from 50 to about 300pounds per square inch for a time suflicient to give the desiredconversion to aromatics. as will be explained in detail in a latersection. The product fromsaid first catalytic stage is then separated bydistillation into a light gas fraction consisting largely of hydrogenand methane, which may be employed directly as the carrier gas alreadymentioned or further separated to give a butane fraction which may beremoved from the process for other well known uses, a liquid fractionboiling above butane up to about 180 F., which may be either recycledfor further processing or removed from the process for use elsewhere, asmay be desired, a higher boiling liquid fraction from 180 F. to about227 F. which is recycled to the first catalyst stage for furtherprocessing, a liquid fraction boiling between about 227 F. and 232 F.which is charged to the second catalyst stage, and a bottoms fractionboiling above about 232 F. which may be used as a source of higherboiling aromatics or otherwise disposed of as desired. The narrowboiling cut from 227 F. to 232 F. is charged to the second stagecatalyst system vtogether with a carrier gas containing hydrogen andunder substantially the same conditions as already described for thefirst stage operation except that the rate of charge, and hence the timeof reaction in the second stage, may be varied somewhat to accommodatethe particular stock which is undergoing treatment so as to produce ailnal toluene rich product of the desired characteristics. This crudetoluene can then be separated by ordinary good fractional distillationwith the production of a toluene product that may directly, or after aslight acid treatment, be satisfactorily subjected to nitration or suchother chemical use as desired.

While the process as described herein contemplates two separate catalyststages arranged in series with an eiiicient fractional distillationstage between them, it will be apparent to those skilled in the art thatby providing adequate storage facilities the same ultimate result can beobtained by preparing and storing the toluene rich 227 to 232 F. cut andsubsequently passing it through the same catalyst stage in which it wasprepared but under the conditions for second stage operation, as alreadydescribed. This second stage treatment is in no sense equivalent to arecycle treatment through the first stage since it is critically andpositively a treatment of the desired product separated as far aspossible from all other materials instead of being added to fresh feedas in a typical recycle operation.

The diluting or carrier gas may, as mentioned above, be the gas producedin the process or a more or less similar gas derived from any otherconvenient source. We have found, however, that it should contain atleast 40% by volume ci hydrogen and preferably above 50% in order thatthe most efficient u-se of the catalyst may be realized. We have foundit desirable to employ this carrier gas at the rate of from about 2,000to 12,000 cubic feet. measured under standard conditions of temperatureand pressure, per barrel of the liquid hydrocarbon charged. The ratio ofgas to hydrocarbon charge on a molecular basis is then between about twoto one and about twelve to one which. when the carrier gas contains 50%or more of hydrogen, would thus give a molecular ratio of hydrogen tohydrocarbon of from at least one to one to about six to one. Higherratios may, of course, be employed but without substantial improvementin results, while lower ratios are to be avoided since at dilutionsbelow about two to one the proportion of the charge which is lost tocoke and gas increases very rapidly.

In addition to the significant ratio of diluent gas to naphtha justexplained, we have also found that the proportion of hydrogen in thediluting gas at any given total pressure or, more broadly, its partialpressure in the reaction mixture is extremely significant to thesatisfactory converassasas (45 and 150 pounds per square inch). Whilethe total pressure on the system doesnot appear to be particularlycritical. it will be seen, from what has already been said. to besubstantially nxed by the limits of dilution prescribed and by thedesirable partial pressures of hydrogen. to a range between about 50 and500 pounds per square inch and usually to between about 100 and 400pounds per square inch.

With the hydrogen rich stocks consisting substantially of paramns,naphthenes and low boiling aromatics which are preferred for the processof the present invention, it has been found that the process gas asproduced in the first catalyst stage usually contains suillcienthydrogen that it may be employed without further adjustment as thediluent gas. When, however, it is desirable to recover from the firststage gas butanes, and possibly also propane for use in other processes,the concentration oi hydrogen in the remaining gas is, of course,increased and the gas is therefore rendered even more suitable for useas the diluent or carrier agent in our process. With the temperature,total pressure, partial pressure of hydrogen and degree of dilution ofhydrocarbon charge by inert gas regulated substantially within theranges just specied, the extent of conversion in the catalyst stages maybe varied as desired by adjusting the time of the reaction ox', moredirectly, the rate at which the hydrocarbon charge is fed to theprocess.

We have found that in producing toluene from a California straight-rungasoline, the toluene cut should be charged to the first catalyst stageat such a rate as will give a debutanized product containingapproximately 40% of aromatic compounds in order that the highestover-all yield of toluene from a given amount of charge may be producedwith the least operating diiiculty. With the more active physicalmodifications of the above-mentioned catalysts and the conditions ofoperation as already given, this degree of conversion is realized bycharging from about 0.7 to 3.0 volumes of hydrocarbon (measured asliquid) per volume of catalyst (including voids) per hour. While it istrue that with a lower conversion in the first stage a slight increasein the over-all yield of toluene may be realized, this is possible onlyWith a substantial reduction in the capacity of any given plant. With aconversion in the rst catalyst stage to give more than about 40% ofaromatics in the debutanized product, the ratio of toluene to gas andlight liquid, boiling below about 180 F., is found to decrease rapidlyand hence the yield of toluene per unit of charge is reducedproportionally by such higher conversion in the rst stage.

While it is possible that this optimum conversion in the first stage forhighest plant efliciency and highest ultimate yield o1 toluene might beslightly different for charging stocks varying widely the nature andrelative proportions of 'the components in the 180 to 250 F. boilingrange, such variations will be found to be readily determinable andhence are believed to oe comprehended by our invention.

The conditions to be maintained in the second catalyst stage al e, asalready indicated, substantially the same as employed in the firststage, so long as equivalent type catalysts are used in both. However,in addition to the possible slight variation in hydrogen concentrationin the carrier gas mentioned above, it may also be desirable to alterthe feed rate 'to the second stage slightly to pro- 6 duce the absolutemaximum yields of toluene with minimum loss of charge to gas and coke.

Instead of making adjustments in the feed rate. while maintaining aconstant average temperature of reaction, in order to secure the desireddegrec of conversion ineither ilrst or second catalyst stages, it hasbeen found more desirable under certain circumstances to maintain a nxedfeed rate and to adlustthe inlet temperature to the catalyst chamber togive the desired conversion. the temperature being readlusted as may benecessary to compensate for fluctuations or changes in catalyst activityin order to maintain the extent of conversion constant throughout theoperation. Ordinarily it will be found most convenient to fix the pointof operating temperature control at the inlet to the catalyst chamber,the temperature there being adjusted to that which is found, with agiven apparatus and stock, to give the desired degree of conversion.This point of temperature control is chosen since the temperature at anypoint within the catalyst chamber is a much less definite quantity dueto the rather large temperature drop through the catalyst due toendothermic heat of reaction.

One preferred embodiment of the process of the present invention willnow be explained with reference to the iigure of the attached drawing.It will be appreciated that this figure is a scheimatic representationor flow diaphragm of the process and has no reference whatever to thespeciiic apparatus in which the process may be eifected. All valves,condensers, heaters and like conventional items of equipment have beenaccordingly omitted.

For the production of toluene the liquid hydrocarbon charge to the firststage of the process is preferably a closely fractionated cut from anaphthenic petroleum having a boiling range from about to 235 F. Thischarge may be passed through line I to the first stage heating zone 5 towhich are also passed recycle gas from line 3, light recycle liquid fromline I3, heavy recycle liquid from line 3l and extraneous hydrogen fromline 2 when necessary. The preferred ratio of recycle gas to totalliquid feed to the catalyst chamber is of the order of 6,000 cubic feetper barrel. At this ratio it is desirable that the recycle gas shouldcontain at least 40%, and preferably above 50%. of hydrogen and that themolecular ratio of hydrogen to liquid hydrocarbon charge be of the orderof 3:1. The extraneous hydrogen added through line 2, as alreadymentioned, is thus employed whenever necessary to bring the hydrogencontent of the carrier gas entering the heating zone within this desiredrange.

The heated mixture from zone 5 is passed through line 6 to the rstcatalyst lstage represented `by drums I and I which contain a pelleted,coprecipitated, molybdenum-aluminum catalyst. A pressure of about 200pounds per square inch is maintained in the reaction zone with an inlettemperature of between 900 and l025 F. 'Under these conditions and withthe charging material indicated, the desired extent of reaction can beeected at a charging rate of about 0.8 to 1.0 volumes of liquid chargeper volurne ci catalyst containing space per hour. The reaction mixtureis passed from the catalyst zone through line i (i) to a iirst stageliquid stabilizer wherein the sutane and lighter components of thecharge may be separated from the normally liquid components, the lighttraction being passed through line t for subsequent treat@ ment, asdescribed later herein. while the normally liquid product ispassedthrough line l to a nrst stage still, ii. This rst stage still mayin fact consist of one or several separate stills as may be found moreconvenient and economical in the preparation of the desired close-cutfractions. A low boiling fraction from start to about 180 F. willusually be taken of! and removed from the system. A side stream boilingfrom 180 to about 227 F. may be returned through line Il as a lightrecycle stock to the ilrst heating zone i. A crude toluene fractionboiling from about 227 to 232 F. will be recovered for use as `thecharging material to the second stage of the process while the fractionboiling above 232 F, may be removed through line Il and sent forward toa xylene stillfor the recovery of the higher boiling aromatica.

Recycle gas is charged to the second heating zone il from line I6,additional hydrogen, when required, from line I1 and second stagerecycle liquid from line 2B. The recycle or carrier gas to the secondstage need not be quite so rich in hydrogen as the gas in the ilrststage but in any event it should contain at least of hydrogen, andpreferably at least 30%. 'I'he rate of charging gas to the second stagewill usually be substantially the same as in the first stage, that is,about 6.000 cubic feet per barrel of crude to1uene charged from line i4.A pressure of about 200 pounds per square inch and an inlet temperaturebetween about 950 and 1025 F. are maintained in the second stage of theprocess. Here again, the liquid feed rate is of the order of 1.0vol./vol./hr. when an active coprecipitated molybdenum-aluminum catalystis employed.

The product from the second catalyst stage II (II') is passed throughline 20 (20') to the second stage liquid stabilizer 2| wherein thebutane and lighter gases are separated from the normally liquidcomponents, the former being discharged from the system or passedthrough line 22 to line 9 for treatment together with the gaseousproduct from the iirst stage, while the normally liquid fraction isdischarged through line 23 to toluene still 24. The toluene still 24may, as in the case of the first stage still, actually consist of one ormore vstills conveniently arranged to most eillciently prepare thedesired close fractionated cuts. A start to about 220 F. cut may betaken overhead from this still through line 25 to line i0 and still ii.A 220 to 230 F. fraction may be prepared for return through line 26 assecond stage recycle liquid to the second stage heating zone i8. In someinstances it may be preferable to include this latter cut with the lightcut, whereupon the combined start to 230 F. fraction would be passedthrough line 25 as already described. A 230" to 232 F. fraction, whichwill now contain 99%-ltoluene, is discharged through line 21 while thebottoms boiling above 232 F. may be discharged from the system or sentthrough line 28 to the xylene still 29 for recovery of such higherboiling aromatics as may be present.

The xylene still 29, in which the bottoms fractions from first stagestill Il and toluene still 24 are combined, will usually be operated togive three fractions: A 235 to 275 F. cut which is removed at 30 anddischarged from the system, sent to the absorber 32 or sent by line 3las heavy recycle liquid to the ilrst heating zone 5, a 275 8 which isremoved at 24 and discharged from the system or sent through line I5 toabsorber 22.

The absorber 32 is employed f or separating the butanel and sometimesalso the propane fractions from the gases produced in the first andsecond stage treatments. These heavier gaseous hydrocarbons are absorbedin a sponge liquid which may be a hydrocarbon liquid Provided especiallyfor that purpose or may, as already herein indicated, be theintermediate and/or heavy liquid fractions produced during the reaction.such as the bottoms cut from the ilrst stage or toluene stillsor theoutside fractions from the xylene still. The saturated sponge liquidfrom absorber 32 may 'oe removed through line 38 and sent to a recoverysystem, not shown. or sent through line 3l to the ilrst heating zone 5as heavy recycle liquid. The gases leaving the absorber at 31 are passedby line I8 to the second heating zone i8, by lines i6 and 3' to therecycle gas holder 38, or by lines I6 and I to the first heating zone 5.

While, for convenience, the drawing has shown both the first and secondcatalyst stages as composed of two catalyst drums, so arranged that thecatalyst in one drum may be regenerated while the other is on stream. itwill be appreciated that any more convenient number of drums may beemployed. For instance, when on stream periods shorter than about onehour are desirable, it may be found necessary to provide three or moredrums for each catalyst stage in order that the complete cycle of onstream and regeneration steps may proceed with out interruption. 'I'heinert gases necessary for purging the catalyst drums prior to theirregeneration, and necessary also for diluting the air used in reburningthe catalyst, are stored in purge gas holder 39 which is shown withappropriate connections to the catalyst drums of both stages of theprocess. In general, it is desirable in regenerating catalysts of theclass em ployed in the present process to dilute the air employed inregeneration suillciently that temperature in the catalyst may be heldbelow the point at which appreciable inactivation of the more sensitivecatalysts may occur. This temperature is about 1200 F. Instead ofeifecting this temperature control by ilue gas recycle, it may equallywell be effected by the now well known method of building into thecatalyst chamber heat dissipating means such as flns, fiues and tubesfor circulating a cooling fluid.

In order that the progressive increase in toluene content of thehydrocarbon liquid as it passes through the process of the presentinvention may be better visualized, the approximate percentage oftoluene contained in the liquid passing through lines I0, I4, 23 and 21has been indicated on the drawing. While these values may vary somewhatwith different charging stocks, they may be substantially regulated bycontrolling the conversion effected in the rst stage so that the liquidpassing through line I0 will contain about 40% aromatics. With theaverage naphthenic stock used as a basis for the foregoing description,the crude toluene charge (line i4) to the second stage will then containapproximately total aromatics, the second stage product (line 23)passing to the toluene still will contain about 96% toluene and thefinal product discharged through line 21 will be substantially pure99%+) toluene. For con venience in visualizing theA process, thesefigures have been indicated enclosed in circles at the appropriatepoints on the drawing. The over-all yields of toluene that have thusbeen obtained vary from about 32 to 42% by volume o! the liquid charge.

The process oi our present invention may be further illustrated byreference to the following specific examples in which runs employingdifierent catalyst combinations in the two stages of the process aregiven. The detailed data for all three examples are collected in thetable.

man1

A California petroleum fraction having an A. S. T. M. boiling range from196 to 236 l". was employed in a two-stage process for tolueneproduction in which a coprecipitated molybdenumaluminum catalyst wasemployed in both catalyst stages. While toluene yield was almostidentical with that in Example l. the total liquid recovery was 3.5%higher (being 84.1% as compared with 80.6%) and the loss to coke and gascorrespondingly lower.

Examms 3 Product from the ilrst stage treatment of Example 2 whensubmitted to a second stage employing a coprecipitated vanadium-aluminumcatalyst gave the results indicated. It will be noted that the over-allresult is not quite as good as with the coprecipitatedmolybdenum-aluminum catalyst in both stages but is somewhat better thanthe supported molybdenum oxide in both.

10 While the foregoing discussion and examples have been directedparticularly to the production of toluene from a naphthenic Californiastock, it is equally possible to,produce the other low boilingaromatica. such as benzene. ethyl benzene and xylene. iromvtheappropriate fractions .of such a stock or to produce any of the 4 lowboiling aromatics as desired from such other petroleum stocks as may beavailable. In general, it has been ioimd that the less naphtheniccharging stocks give better results at somewhat lower total pressureswhen the quantity and composition oi the recycle gas is variedaccordingly to give the desired ratio of hydrogen to charge in thereaction zone.

Having now described and illustrated a novel two-stage catalyst processcomprising a particular combination of catalytic and distillation stepsfor the production of substantially pure aromatic liquids from selectedpetroleum fractions, wo claim:

1. Process for the production oi toluene which comprises subjecting afraction from a naphthenic petroleum boiling in the range from about 180to about 235 F. to the action of a coprecipitated molybdenum-aluminumcatalyst at a temperature between about 900 and 1025 F. under a totalpressure oi about 200 p. s. i. and in the presence of a carrier gascontaining at least 40% hydrogen. said carrier gas being in the ratio ofabout 6000 cu. it. per barrel of liquid charge, for a time sufficient toproduce a debutanized liquid product containing about 40% of aromatica,iractionally distilling said product to produce a sharp cut boilingbetween about 227 and 232 F., subjecting said sharp cut to a secondcatalytic treatment in the absence of said fraction and underapproximately the same conditions as prevailed in the rst catalyst stagetor a time suillclent to produce a debutanized product containing above90% aromatics, and subjecting said product to an emclent fractionaldistillation to produce a fraction containing at least 99% toluene.

Tam

Data from two-stage toluene process Example l Example 2 Example 3 Feed:

A. P. I. Gravity 5 67. 9 57.9 Annina Point, F. 115 116 Per centAromatics 7. 0 6. 0 6. 0 A. 8. T. M. Start 192 196 196 199 200 2(1) 20m0 200 200 203 203 293 m6 210 210 210 E. P 239 236 236 First-StageOperation:

Catalyst. MoOs on AhOa Co-ppt. Mo-Ai Co-ppt. Mo-Al Temp F.. aver 000Temp F.. et.-. 985 985 Temp.. F. Outlet 890 S90 Press., p. u. i 20o 20o20o Rate v.lv.{hr 1.0 i. 0 l. 0 @as aecye e s, ooo s, ccc c, occHsontent, 68 70 70 Second-Stage Operation:

Catal MoOla 3) A1305 Co-ppt. Mo-Al Cappt. "V-Al 978 '990 985 97D 200 200mi) l. 0 l. 0 il. 8 6, C00 6, C00 00S il 30 27 l 5 lfl. 9 15. 4 I l. 02l. l l. 3 8 20. Q 30. 3 73 l1. l. 0 l. 2 Ifluere 40. 3 4G. 2 38. 9

2. Process as in the preceding claim wherein the catalyst in the firststage is a coprecipitated molybdenum-aluminum and in the second stage acoprecipitated vanadium-aluminum composition.

3. Process for the production of substantially pure liquid aromaticsfrom naphthenic petroleum stocks which comprises subjecting a selectednarrow fraction thereof boiling within the range from about 180 to 235F. to the action of a dehydrogenation type catalyst at superatmospherictemperature and pressure in the presence of a carrier gas containingfree hydrogen, collecting the liquid product produced, separating fromit by extreme fractionation a c ut boiling between about 227 and 232 F.which contains a maior proportion oi' toluene and a bottoms fractionboiling above 232 F. containing higher boiling aromatics, subjecting thetoluene containing fraction to a second stage of catalytic treatmentwith a dehydrogenation type catalyst for the conversion of nonaromaticcompounds collecting the liquid product, separating substantially puretoluene from said product by fractional distillation, collecting abottoms fraction boiling above about 232 F., combining said bottomsfraction with the bottoms fraction segregated from the iirst stageproduct and separating a substantially pure xylene therefrom.

4. Process for the production of substantially pure toluene from anaphthenic petroleum distillate which comprises subjecting a fractionfrom said distillate boiling within the range from about 180 F. to about235F. to the action of a coprecipitated compound catalyst containingcombined molybdenum and aluminum at a temperature between about 900 and1050 F. and a pressure of between 50 and 300 p. s. i. in the presence ofa recycle gas containing free hydrogen, collecting the liquid productformed, separating from said liquid product by extreme fractionation, atoluene rich fraction containing substantially only hydrocarbonimpurities that are inseparable from toluene by said fractionation,subjecting said crude toluene fraction in the absence of said naphthenicpetroleum distillate to the action of a coprecipitated catalyst of thesame type and under approximately the same conditions as prevailed inthe first catalyst stage whereby the hydrocarbon materials associatedwith the toluene are converted to substances that are separable from thetoluene by fractional distillation and effecting said separation toproduce toluene of nitration grade.

5. In the process for producing substantially pure toluene in which acharging stock consisting essentially of a naphthenic petroleumdistillate boiling within the naphtha boiling range is catalyticallyaromatized by subjection to the action of a dehydrogenation catalystcomprising coprecipitated molybdena and alumina at a temperature fromabout 800 to 1050 F. in the presence of a carrier gas containing atleast 40% by volume of hydrogen, at a total pressure of the order offrom 50 to 500 pounds per square inch, at a partial pressure of hydrogenfrom about to 300 pounds per square inch and at a space velocity of 0.7to 3.0 Volumes of liquid hydrocarbons charged per volume of catalystspace per hour and thereby a resulting product is produced includingtoluene and some other constituent undesired in the final product andinseparable from said toluene by fractional distillation, theimprovement for producing substantially pure toluene which comprisesfractionally distilling said resulting product and thereby separatingtherefrom a narrow cut containing substantially only said toluene inmajor proportion and constituents inseparable therefrom by fractionaldistillation and subjecting said narrow cut containing said toluene inthe absence of said distillate to the action oi a catalyst comprisingcoprecipitated molybdena and alumina at a temperature from about 800 to1050 F. in the presence of a carriergas containing at least 40% byvolume of hydrogen and at a total pressure of the order oi' from 50 to500 pounds per square inch and at a partial pressure oi' hydrogen fromabout 30 to 300 pounds per square inch at a space velocity of 0.7 to 3.0volumes of liquid'hydrocarbons charged per volume of catalyst space perhour to transform said cut and render said toluene separable from thetransformed product by fractional distillation. and fractionallydistilling to separate substantially pure toluene.

6 Process as denned in claim 5 in which both of said catalyticconversion steps have a temperature of between 900 and 1050 F.. a totalpressure of from 100 to 400 pounds per square inch, l. hydrogen partialpressure of from 45 to 150 pounds per square inch, and said carrier gascontains at least 50% by volume of hydrogen.

7. Process as deiined in claim 5. in which said' narrow cut has aboiling range between about 227 F. and 232' F.

8. Processssdeiinedinclaim5,inwhichseid naphthenic petroleum distillateis a straight run distillate.

9. Process as denned in claim 5, in which said naphthenic petroleumdistillate has an approximate boiling range of 180 to 235 1l'.

l0. In the process for producing a substantially pure aromatic compoundin which a charging stock consisting essentially of a naphthenicpetroleum distillate boiling within the naphths. boiling range iscatalytically aromatized by subiection to the action of adehydrogenation catalyst oomprising coprecipitated molybdensl andalumina at a temperature from about 800 to i050 l". in the presence of acarrier gas containing at least 40% by volume of hydrogen, at s totalpressure oi the order of from to 500 pounds per square inch, at apartial pressure of hydrogen from about 30 to 300 pounds per square inchand at a space velocity of 0.7 to 3.0 volumes of liquid hydrocar- 50bons charged per volume of catalyst space per es ing coprecipitatedmolvbdena and alumina at a temperature from about 800 to 1050 F. in thepresence of a carrier gas containing at least 40% by volume of hydrogenand at a total pressure of the order of from 50 to 500 pounds per square7 inch and at a partial pressure oi' hydrogen from about 30 to 300pounds per square inch at a space velocity of-0.7 to 3.0 volumes ofliquid hydrocarbons charged per volume of catalyst space per hour totransform said cut and render said arou matic compounds separable fromthe transformed 13 product by fractional distillation, and fractional-1y distiiling to separate said aromatic compound. 11. Process as definedin claim 10, in which the catalyst in at least one of the catalyticstages comprises coprecipitated vanadia and alumina.

12. Process as defined in claim 10, in which said aromatic compound is axylene.

WILLIAM H. CLAUSSEN. THOMAS M. POWELL.

REFERENCES CITED The illowing references are of record in the ie ofthlspatent:

UNITED STATES PATENTS Huppke Nov. 4, 1941 14 Number Namo Date 2,270,715Layng et al Jan. 20, 1942 2,271,751 Vissel et ai. II Feb. 3, 19422,285,727 Komarewsky June 9, 1942 1,441,341 Govers `Jan. 9, 19232,143,472 Boultbee Jan. 10. 1939 2,222,128 Wagner Nov. 19, 19402,279,198 Huppke II Apr. 7, 1940 2,304,183 Layng et al. II Dec. 8, 19422,313,346 Kaplan Mar. 9, 1943 2,322,863 Marschner June 29, 19432,288,866 Hoog July 7, 1942 2,344,318 Mattox Mar. 14, 1944 2,349,045Layng et al. IH May 16, 1944 2,349,826 Layng May 30, 1944 OTHERREFERENCES Zelinsky et al., Ind. Eng. Chem. 27 1209-11 (1935).

